A breathing mask is a device used to enable breathing in environments where such would be difficult or impossible without mechanical aid. Typically, a breathing mask incorporates an inlet valve which controls the flow of gas for breathing between a supply of breathing gas and the user of the breathing mask. A lung-governed valve controls the flow of gas through the inlet valve via the respiration of the user.
A diaphragm divides the lung-governed valve into an inner chamber at a pressure corresponding to the pressure within the breathing mask and an outer chamber at a pressure corresponding to the pressure in the environment. The diaphragm is coupled to a mechanism which opens and closes the inlet valve. The user's respiration creates a pressure differential between the inner and outer chambers of the valve which, in turn, causes displacement of the diaphragm thereby controlling the inlet valve closure mechanism.
A lung-governed valve of this type is described in German Patent No. DE 35 39 669 A1. In that device, the diaphragm controlling the inlet valve lever has at its central point a cam projecting outwardly into the outer chamber. A tilt lever is pivoted to the outer chamber casing and is clamped by transversely tensioned spring elements to the outer chamber so that the tilt lever is movable in a tilting joint. The tilt lever is movable out of an idle position into a first pressure position, exerting force on the diaphragm, and into a second stand-by position, lifting the diaphragm off the valve lever by engaging the cam and moving it and the diaphragm through a predetermined stroke. Because of the transversely tensioned spring elements, which are pivoted to the shorter end of the tilt lever, the end position of the tilt lever may be unstable. Subjection of the valve to external stress may cause the tilt lever to tilt from one position to the other. This instability is particularly disadvantageous when the control diaphragm is in the stand-by position. In this position, external vibration could tilt the lever, entraining the control diaphragm and opening the inlet valve via the valve lever. The limited amount of breathing gas available to the person using the apparatus can thus be inadvertently lost.
It would be desirable, therefore, to develop a lung-governed valve with an improved structural design wherein the valve is protected from accidental release or switching on when in the stand-by position.